1. Field of the Invention
The present invention relates to a cylinder apparatus for a hydraulic lift jack with a transmission device, in particular, to a cylinder apparatus for a hydraulic lift jack with a transmission device, in which the lift jack can be accurately located at the lower portion of an object to be loaded in a narrow place by constructing an upper end portion of the lift jack such that forces can be concentrated on any one point, and a transmission device is installed to adjust an ascending and descending velocity of the lift jack by pumping the fluids so that the ascending velocity of the lift jack can be increased progressively at high velocity when the load has not been applied, and the ascending velocity of the lift jack can be increased strongly at low velocity when the load has been applied, at the time of the ascending and descending operations of the lift jack.
2. Description of the Prior Art
As generally known in the art, a jack is a device used for repairing a vehicle in case of small disorders such as tire punctuations, and so on arising urgently at the time of driving. For instance, the jack is used to lift up a wheel of a vehicle and to exchange the punctuated tire, in case of tire punctuation. Accordingly, it is one of those instruments equipped always in the vehicle so that it can be used, if required.
The jack can be classified into various types based on its shape, however, the jack of the present invention relates to a jack operated by hydraulic pressure, in particular to a jack with a hydraulic cylinder for pumping the hydraulic pressure.
As described above, if the disorder arising during the driving is so big that it cannot be repaired simply in site, or it requires an aid from the special repairman, substantial repair is performed in the repairing place.
For instance, when a repair is performed to dismantle or exchange the heavy parts such as an engine or a transmission, and so on, repair is performed at the special repairing place. In this instance, the lift jack apparatus is employed to ascend and descend the heavy parts safely and conveniently.
One of such conventional lift jack apparatus shown in FIG. 1 is disclosed in Korean Patent application Laid open No. 1999-37434 (published on Jun. 25, 1999). As shown in FIG. 1, an X-shaped beam of the conventional lift jack apparatus rotates around a pivot axis to thereby ascend and descend free end of it by means of an extended length, when the piston rod of the hydraulic cylinder is extended to thereby make the length of the piston rod extend.
It is designed that an upper plate (supporting plate) is installed at upper end portion utilizing such principle so that it can lift a vehicle loaded thereon.
As shown in FIG. 2, a modified type of lift device can be constructed by an x-shaped beam and a hydraulic cylinder, and in addition, various types of lift jack device can be constructed, however, they also cannot support parts loaded on the narrow space because the areas of all the upper plates are very big and large.
For instance, a lift jack device can be used to ascend or descend a transmission or an engine when they are assembled or dismantled from the vehicle body at the time of repair and maintenance of them. However, it is difficult to locate the upper plate accurately on a lower surface of an object because the area of the upper plate is big and large, further it is complex in that surrounding parts interfering the upper plate should be dismantled and removed at the time of locating the upper plate.
Also, as shown in FIG. 2, with regard to most of the conventional hydraulic lift jack device (if necessary, wheels can be installed), it is very inconvenient because the loaded objects should be descended from the upper plate of the jack device to ground or ascended from the ground to the upper plate, on condition that the upper plate of the lift jack device is located at about a height of 90  when the upper plate is lowered to its maximum state. Also, it is very inconvenient to ascend and descend the very heavy objects from the ground to the upper plate located at the height of 90. Further, it is inconvenient because separate equipment such as a hoist is required at the time of transporting the object loaded on the upper plate to the other place.
Accordingly, an invention disclosed in Korean Patent application No. 2003-72709 filed by the same applicant of this application has been developed to overcome such shortcomings described above. In this invention, a lift jack device is constructed to concentrate forces on any one place of the upper plate so that a support member can be accurately located at lower surface of the loaded object in spite of the narrow space.
However, although the hydraulic lift jack device has been constructed such that a pair of X-shaped beams are ascended concurrently by pumping fluids into a sub-cylinder by means of a main hydraulic cylinder, it caused a problem of consumption of unnecessary time in a pumping operation because repeated pumping operation is required till the upper end of the jack reaches lower surface of the object to be lifted by always supplying a predetermined volume of fluids.
In addition, if it is required to repair (dismantling/assembly) the engine or the transmission, bolts are dismantled or assembled after the vehicle is lifted to a predetermined height and the bottom surface of the engine or the transmission device is supported by the lift jack. Therefore, a number of repeated operations of the pedal for pumping fluids are required so that upper end of the jack reaches at the lower surface of the object to be lifted at the time of initial operation of the lift jack. It is inconvenient because working velocity becomes slow due to relatively great number of pumping. Also, it is inconvenient in that bolt engagement work is difficult in the narrow space because a length of the object ascended through the pumping operation is long, so that an axial line of the corresponding engagement holes and the through-hole formed at the object is not aligned, when the heavy object is lifted for assembly.
As described above, in the conventional lift jack device, it is necessary to operate the hydraulic cylinder many times till the jack reaches at the lower surface of the object, as the volume and velocity of the hydraulic pumping are always linear. Also, it is difficult to adjust the ascending height of the object accurately at the time of ascending the object, after the upper end of the jack reaches the lower surface of the object to be lifted. Additionally, it is necessary to apply lots of forces to operate the pedal for pumping the fluids to activate the hydraulic cylinder. Accordingly, it is necessary to develop a hydraulic cylinder in which workers can selectively adjust the operations of the pedal, volume and velocity of the fluid pumping based on the operation conditions.